New laser-trimmed film resistor structures for very high stability requirements

The drift with time and/or temperature of laser-trimmed film resistors limits the effective accuracy attainable form laser-trimmed resistor circuits. This accuracy is dependent on the geometries of the film resistors and on the trimming process. Novel film resistor structures that practically and significantly improve the effective ultimate accuracy attainable with laser-trimmed film resistors over both time and temperature are proposed. The structures are evaluated using computer simulations. This technique is substantiated with an example that shows an improvement in resolution of 4 bits when compared to that attainable with conventional bar resistors